Modeling and Flowsheet Design of an Am Separation Process Using TODGA and H₄TPAEN

Recycling americium from spent fuels is an important consideration for the future nuclear fuel cycle, as americium is the main contributor to the long-term radiotoxicity and heat power of the final waste, after separation of uranium and plutonium using the PUREX process. The separation of americium alone from a PUREX raffinate can be achieved by co-extracting lanthanide (Ln(III)) and actinide (An(III)) cations into an organic phase containing the diglycolamide extractant TODGA, and then stripping Am(III) with selectivity towards Cm(III) and lanthanides. The water soluble ligand H4TPAEN was tested to selectively strip Am from a loaded organic phase. Based on experimental data obtained by Jülich, NNL and CEA laboratories since 2013, a phenomenological model has been developed to simulate the behavior of americium, curium and lanthanides during their extraction by TODGA and their complexation by H4TPAEN (complex stoichiometry, extraction and complexation constants, kinetics). The model was gradually implemented in the PAREX code and helped to narrow down the best operating conditions. Thus, the following modifications of initial operating conditions were proposed: • An increase in the concentration of TPAEN as much as the solubility limit allows. • An improvement of the lanthanide scrubbing from the americium flow by adding nitrates to the aqueous phase. A qualification of the model was begun by comparing on the one hand constants determined with the model to those measured experimentally, and on the other hand, simulation results and experimental data on new independent batch experiments. A first sensitivity analysis identified which parameter has the most dominant effect on the process. A flowsheet was proposed for a spiked test in centrifugal contactors performed with a simulated PUREX raffinate with trace amounts of Am and Cm. If the feasibility of the process is confirmed, the results of this test will be used to consolidate the model and to design a flowsheet for a test on a genuine PUREX raffinate. This work is the result of collaborations in the framework of the SACSESS European Project

Modeling and Flowsheet Design of an Am Separation Process Using TODGA and H₄TPAEN

Recycling americium from spent fuels is an important consideration for the future nuclear fuel cycle, as americium is the main contributor to the long-term radiotoxicity and heat power of the final waste, after separation of uranium and plutonium using the PUREX process. The separation of americium alone from a PUREX raffinate can be achieved by co-extracting lanthanide (Ln(III)) and actinide (An(III)) cations into an organic phase containing the diglycolamide extractant TODGA, and then stripping Am(III) with selectivity towards Cm(III) and lanthanides. The water soluble ligand H4TPAEN was tested to selectively strip Am from a loaded organic phase. Based on experimental data obtained by Jülich, NNL and CEA laboratories since 2013, a phenomenological model has been developed to simulate the behavior of americium, curium and lanthanides during their extraction by TODGA and their complexation by H4TPAEN (complex stoichiometry, extraction and complexation constants, kinetics). The model was gradually implemented in the PAREX code and helped to narrow down the best operating conditions. Thus, the following modifications of initial operating conditions were proposed: • An increase in the concentration of TPAEN as much as the solubility limit allows. • An improvement of the lanthanide scrubbing from the americium flow by adding nitrates to the aqueous phase. A qualification of the model was begun by comparing on the one hand constants determined with the model to those measured experimentally, and on the other hand, simulation results and experimental data on new independent batch experiments. A first sensitivity analysis identified which parameter has the most dominant effect on the process. A flowsheet was proposed for a spiked test in centrifugal contactors performed with a simulated PUREX raffinate with trace amounts of Am and Cm. If the feasibility of the process is confirmed, the results of this test will be used to consolidate the model and to design a flowsheet for a test on a genuine PUREX raffinate. This work is the result of collaborations in the framework of the SACSESS European Project

Elaboration d'un estimateur d'état pour l'aide au pilotage de procédés de traitement du combustible irradié

International audienceLe traitement du combustible irradié est réalisé à l’aide du procédé PUREX. Aprèsdissolution des pastilles de combustible, les éléments d’intérêt sont séparés puis purifiés en vue deleur recyclage. Le code PAREX, développé par le CEA, simule l’évolution des paramètres duprocédé au cours du temps et a aidé à la conception des ateliers de purification de l’usine de LaHague.L’objet de la thèse est d’estimer en temps réel un ensemble de paramètres caractérisantl’état du procédé grâce à l’exploitation des mesures disponibles sur l’installation, et plusparticulièrement celles représentatives de l’état du procédé nommés indicateurs d’état. Dans lecas des opérations d’extraction-lavage, la charge en uranium et plutonium du solvant est unfacteur déterminant : elle doit être suffisamment élevée pour obtenir une bonne décontamination,sans être excessive afin d’éviter d’altérer le rendement de récupération des cations d’intérêt. Lasimulation du procédé à l’aide du code qualifié PAREX, permet de relier les paramètresopératoires (débits et caractéristiques des solutions d’entrée, etc) aux différentes mesures de suivireflétant l’état du procédé et d’accéder précisément aux paramètres d’état recherché. L’objectif dela thèse est ainsi de bâtir un algorithme réalisant l’estimation des indicateurs d’état du procédé etde vérifier leur cohérence.Pour construire l’outil, deux étapes majeures se distinguent :- la réconciliation des données de l’installation afin de consolider et rendre cohérent l’ensemble dujeu de données;- l’optimisation de ces données d’entrée pour la bonne estimation des indicateurs d’état grâce aucode PAREX

PAREX, a numeric code for plant operation aid

International audienceThe PAREX code has been widely used for process designused for the flowsheet design of the purification cycles ofthe La Hague plant build for nuclear fuel treatment. Thispaper focused on the use of the code as an aid for plantoperation through two application examples. The first oneis related to on site flow sheet available marginevaluation of the extraction zone of a first cycle flowsheet. The second example concern the plutoniumstripping operation of a plutonium cycle, where the codehas been used to explain the shift of plutonium leak in thesolvent outlet observed

Modelling of Am stripping step with TODGA - TPAEN

International audienc

Contribution of various techniques to U(VI) and Pu(IV) mass transfer kinetics in liquid-liquid extraction: towards the kinetics regime determination thanks to 3 technics

International audienceIn the frame of the development of Generation IV reactors, CEA is developing an advanced liquidliquid extraction process for the multirecycling of plutonium from the spent nuclear fuels. Thermodynamic data have already been acquired for the modeling of the extraction equilibriums in this process, but accurate kinetic data are also required to simulate the process in short-time contactors and for its scale-up in industrial contactors such as pulsed columns. This paper summarizes the acquisition of mass transfer coefficients of uranium(VI) and plutonium(IV) between nitric acid and a monoamide-based solvent upon extraction with three different techniques: the single drop technique, the Nitsch cell and the rotating membrane cell (RMC). The influence of temperature, nitric acidity, viscosity of the organic phase, the drop size and the nature of the continuous phase (aqueous or organic) on the transfer of uranium and plutonium during the extraction step was studied. The results obtained by the single drop technique showed that U(VI) and Pu(IV) mass transfer constants are quite similar. These data were compared with the literature as with results obtained in similar conditions with the TBP solvent currently used in the PUREX process. They revealed that the kinetics of U(VI) extraction with this monoamide solvent is about three times slower than with TBP, probably because of the higher viscosity of the monoamide-based solvent. The single drop method allowed the most complete study but the other methods brought some qualitative information to better understand the phenomena involved in the transfer of uranium and plutonium with this system. The global results point out that the resistance to the transfer is essentially located in the organic phase and the diffusion process would mainly control the kinetics. An attempt to estimate the chemical and the diffusionnal kinetic constants based on experimental results led also to the same conclusion. These results lead to a better understanding of this extraction system and will help to simulate experimental profiles of uranium and plutonium concentrations measured in continuous tests performed in mixer-settlers or pulsed columns with this monoamide solvent

Extraction performance of monoamide extractants in pulsed columns

International audienceProcess development approach adopted in CEA, based on modelling studies, includes the determination of mass transfer efficiency of the contactors used to perform the different process operations. For monoamide based solvents, tests of several process operations as uranium extraction and back extraction, nitric acid stripping from a uranium loaded solvent were performed in laboratory scale pulsed columns of different heights. The recorded concentration profiles of the species of interest (uranium, nitric acid, ..) were simulated using the PAREX code. Mass transfer kinetics of the species of interest realized with that extractant system permit a very good simulation of the concentration profiles. These results will permit to give the ground data to design the process operation in industrial scale contactors, and will be a guide for further development to enhance if necessary the transfer efficiency of the contactor

A combined process for the selective rare earth recovery and separation from used permanent magnets

International audienceRare earth elements (REE) have become essential for our modern economy, in relation to the development of new energy and communication technologies. Albeit being considered today as the most critical raw materials group with the highest supply risk, the recycling of REE from electronic waste and end-of-life products (permanent NdFeB magnets, Ni-MH batteries etc.) is almost inexistent.[1] Therefore, a large research effort is needed for over-coming the current scientific and technological barriers and improving the recycling efficiency. Innovative, eco-designed processes have to be developed, which require extensive RandD effort from basic research to technological developments.The CEA has gained a world-class expertise in the field of separation processes by hydrometallurgy and pyrometallurgy, several solvent extraction processes being developed and industrially implemented for the nuclear fuel cycle. In this communication, an efficient combined hydro- and pyrometallurgical process aimed at REE recovery and separation from used NdFeB permanent magnets will be presented.[2] The process integrates the mechanical and physico-chemical treatment of NdFeB magnets, followed by a liquid-liquid solvent extraction step for the recovery and intra-separation of REE using a selective extractant with excellent affinity for heavy REE which are today the most expensive REE. Experimental liquid-liquid extraction and modeling data allowing the recovery of a 99.9 per cent pure Dysprosium solution will be discussed in this paper. A subsequent pyrometallurgical treatment via molten chloride salt electrolysis allowed the isolation of pure Dy metal with 80 per cent faradic yield. This is one of the first examples of an effective, closed-loop REE recovery and separation process, starting from magnet scrap down to individual pure REE as metals, which paves the way for future developments in the field.Following this successful demonstration, a new project aimed at the separation of rare earths and nickel from Ni-MH batteries is currently being developed in our department, and preliminary results concerning the evaluation of new molecules for liquid-liquid extraction will be presented in this paper

Apport de la simulation à la conduite d'un procédé de séparation d'éléments proches chimiquement

International audienceLa récupération et la purification de métaux dans des minerais ou des matières recyclables nécessitent dans certains cas le développement de systèmes chimiques d'un haut degré de spécialisation jouant sur des différences ténues de comportement entre les éléments. Ces procédés s'avèrent donc très sensibles aux variations de paramètres opératoires et la réussite de leur mise en oeuvre dans des appareils d'extraction liquide-liquide devient très délicate. La modélisation des phénomènes physico-chimiques mis en jeu et leur simulation dans un code de calcul dédié permet de mieux maîtriser et d'anticiper le comportement du système au cours d'un essai. C'est la démarche suivie par Commissariat aux énergies atomiques et aux énergies alternatives (CEA) pour développer des procédés d'extraction liquide-liquide afin de limiter le nombre d'expériences à réaliser tant au niveau du tube en laboratoire que dans une succession d'appareillages d'extraction liquide-liquide. Dans le cadre du recyclage des actinides du combustible nucléaire irradié, le CEA envisage de récupérer l'américium, pour réduire l'emprise thermique au stockage et afin de le transmuter dans des réacteurs de génération IV. Le procédé par extraction liquide-liquide, EXAm, permet cette récupération sélective, s'avérant délicate du fait du comportement de l'américium très proche de celui d'autres éléments comme notamment le curium ou les lanthanides. Cet article montre la démarche du CEA pour développer EXAm en limitant le nombre d'essais à mettre en oeuvre, tout en atteignant les performances requises malgré la très forte sensibilité du système aux variations de certains paramètres opératoires. La démarche s'appuie sur la modélisation des phénomènes prépondérants en adéquation avec les acquisitions expérimentales, données d'extraction ou de spéciation. Pour la seule première étape du procédé EXAm où l'américium est séparé du curium, le modèle global prend en compte soixante-deux équilibres avec leurs constantes thermodynamiques associées. Ce modèle a été introduit dans le code de simulation de procédé nommé PAREX développé au CEA et cofinancé par AREVA-NC. Ce code permet de calculer, en régime stationnaire ou transitoire, les profils de concentrations des éléments modélisés, dans chaque étage du procédé (mélangeur-décanteur ou extracteur centrifuge dans le cas présent). Grâce à sa rapidité de calcul, des études de sensibilité ont été réalisées en faisant varier un grand nombre de paramètres opératoires. Ceux les plus pertinents pour piloter le procédé ont alors été choisis, et des procédures de mise en oeuvre ont pu être définies en amont puis appliquées lors d'un essai en micro-pilote, en se basant sur les analyses en ligne ou déportées, disponibles sur l'installation. L'ajustement en cours d'essai du débit permettant d'injecter le réactif complexant s'est révélé particulièrement efficace pour atteindre des performances très satisfaisantes de récupération de l'américium malgré la difficulté de séparation intrinsèque de cet élément dans le milieu considéré